1. Field of the Invention
The present invention relates to non-aqueous electrolyte secondary batteries, and more particularly to non-aqueous electrolyte secondary batteries having a pressure-sensitive elastic element.
2. Description of the Prior Art
In recent years, non-aqueous electrolyte secondary batteries have been used not only in compact devices such as mobile phones, notebook PCs, and digital cameras but also as the power source for driving electric vehicles and hybrid vehicles.
When used for the latter application, a plurality of batteries are connected in series using their external electrode terminals so as to produce a high output. Non-aqueous electrolyte secondary batteries are made of highly reactive materials and therefore required to have a much higher safety level when used as large size batteries than when used in compact devices.
In attempts to improve the safety of large size batteries, various techniques have been proposed to install a pressure-sensitive elastic element in a battery (for example, refer to Patent Documents 1 to 8 shown below).
Patent Document 1: Japanese Utility Model No. 04-24262
Patent Document 2: Japanese Patent Unexamined Publication No. 10-241653
Patent Document 3: Japanese Patent Unexamined Publication No. 08-171898
Patent Document 4: Japanese Patent Unexamined Publication No. 08-293301
Patent Document 5: Japanese Patent Unexamined Publication No. 09-55197
Patent Document 6: Japanese Patent Unexamined Publication No. 11-307080
Patent Document 7: Japanese Patent Unexamined Publication No. 11-154504
Patent Document 8: Japanese Patent Unexamined Publication No. 11-329405
These techniques, however, are required to operate the pressure-sensitive elastic element smoothly when the battery internal pressure increases above a certain level. To achieve this, it is preferable that the space on the outer side of the battery is communicated with the atmosphere outside the battery so as to prevent the pressure of the pressure-sensitive elastic element from increasing on the outer side of the battery when the pressure-sensitive elastic element deforms. However, when the space is communicated with the atmosphere outside the battery, the pressure-sensitive elastic element may be damaged by moisture or oxygen entering from the outside of the battery. As a result, the pressure-sensitive elastic element may not operate at a desired operating pressure.
The batteries shown in the aforementioned patent documents are not intended to be connected in series at short distances with other batteries. Therefore, these documents contain no technical suggestion of operating a pressure-sensitive elastic element in combination with the external electrode terminal. Under such circumstances, there is a growing expectation for batteries having a pressure-sensitive elastic element that can operate reliably and speedily when an abnormal stats occurs in a battery, particularly in a large size battery having an external electrode terminal.